1. Field of the Invention
The present invention relates to a combination reflection/transmission-type liquid-crystal display device.
2. Description of the Related Art
Liquid-crystal display devices include a transmission type, in which backlighting is applied to a liquid-crystal cell from the rear and a reflective type, in which external light entering the liquid-crystal display device via the liquid-crystal cell is reflected by the rear surface thereof, the reflected light illuminating the liquid-crystal cell.
In addition, there is a type of liquid-crystal display device which is used as a reflective type display in bright locations and a transmission type of display in dark locations.
Such combination reflective/transmission liquid-crystal display devices are disclosed for example, in the Japanese Unexamined Patent Application publications (JP-A) H10-197865, H10-206844, H10-206846, H10-260402, and H10-260403 in which a translucent sheet is used as a diffuser for backlighting. In the Japanese Unexamined Patent Application publication (JP-A) H10-142601 there is disclosure of the provision of frontlighting at the front surface of the display of a reflective-type liquid-crystal display device, the illumination light provided by this frontlighting or external light being used to illuminate the liquid-crystal cell.
In a liquid-crystal display device, polarized light obtained by passing light through a polarizer is modulated in a liquid-crystal layer. For example, as shown in the typical liquid-crystal display device 1 of FIG. 48, light emitted from a light source 2 strikes a light-absorbing type dichroic linear polarizer 3, the linearly polarized light obtained therefrom then striking a liquid-crystal cell 4.
In the liquid-crystal display device 1 of FIG. 48, polarized light that strikes and passes through the liquid-crystal cell 4 is modulated by application of a voltage to an electrode provided in the liquid-crystal cell 4 so as to change the electric field within the cell, or exits the liquid-crystal cell 4 unmodulated with no electric field, a light-absorbing type dichroic linear polarizer 5 disposed outside the cell passing light of only a particular polarization direction.
Because the light-absorbing type dichroic linear polarizers 3 and 5 pass light polarized in the direction of the transmission axis, and almost completely absorb light polarized in a direction perpendicular to the transmission axis, approximately 50% of the light (nonpolarized light) emitted from the light source 2 is absorbed by the dichroic linear polarizer 3. For this reason, the utilization rate of light in the liquid-crystal display device 1 decreases, making it necessary to have more light from the light source strike the dichroic linear polarizer 3 in order to obtain a sufficient brightness at the surface of the liquid crystal screen.
If the amount of light emitted from the light source 2 is increased, however, there is not only an increase in the electrical power consumed, but also an increase in the heat generated by the light source 2, this leading to the problem of an adverse effect on the liquid crystal in the liquid-crystal cell 4.
Because of this situation, a proposed remedy, as disclosed in a PCT Publication corresponding to JP (Tokuhyo) H4-502524 and in Japanese Unexamined Patent Application publication (JP-A) H6-130424, is a liquid-crystal display device in which a cholesteric liquid crystal layer is used to separate light from a light source by either transmitting or reflecting light of right or left circular polarization, transmitted light of one of the circular polarization directions being caused to strike a liquid-crystal cell, and light of the other of the circular polarization directions being reflected by a reflective sheet as to reverse the direction of rotation thereof, thereby enabling the light to be transmitted through the cholesteric liquid crystal layer, and improving the utilization rate of light.
As disclosed in PCT publication corresponding to JP (Tokuhyo) H9-506985, there is a proposed a liquid-crystal display device in which an extended multilayer film is used to either transmit or reflect nonpolarized light from a light source, thereby dividing the light into two linearly polarized components, the transmitted linearly polarized light being caused to strike a liquid-crystal cell, the reflected linearly polarized light having a polarization direction perpendicular to the transmitted light having its direction of polarization converted by a reflecting sheet, after which it is guided once again so as to strike the extended multilayer film, thereby improving the utilization rate of light.
The liquid-crystal layer in the liquid-crystal display devices disclosed in Tokuhyo H4-502524 and the Japanese Unexamined Patent Application publication (JP-A) H6-130424 shift the phase of light by either xcfx80 (xcex/2) or xcfx80/2 (xcex/4) when no electric field is applied, and do not shift the phase of the light when an electric field is applied, the light emanating from the liquid-crystal layer striking an externally disposed circular polarizer, at which the light is either transmitted or reflected, in accordance with the degree of polarization of the incident light.
In the liquid-crystal display device disclosed in Tokuhyo H9-506985, although there is disclosure of one linearly polarized light component transmitted through an extended multilayer film striking a liquid-crystal cell, there is no disclosure with regard to the retardation at the liquid-crystal layer.
In the above-described combination reflective/transmissive type liquid-crystal display devices, which use a translucent diffusion sheet as a diffusion sheet for diffusing backlighting, the reflectivity of the diffusion sheet is low, resulting in poor display readability, in addition to the problem of low transmissivity.
In the above-described combination reflective/transmissive type liquid-crystal display devices, using frontlighting at the display, there is the problem of insufficient frontlighting intensity (efficiency), this causing poor readability.
Additionally, in the liquid-crystal display devices disclosed in Tokuhyo H4-512524 and in Japanese Unexamined Patent Application publication H6-130424, for the reason noted below, there is an extreme deterioration of readability of the liquid-crystal display and a great loss of contrast, thereby representing insufficient display quality.
More specifically, in the liquid-crystal display device disclosed in Tokuhyo H4-512524, because a circular polarizer directly visible from the outside is disposed outside the liquid-crystal layer, this polarizer being formed by a low-pitch cholesteric film with waveform-dependent reflectivity, approximately 50% of external light striking the circular polarizer is reflected, this reflected light directing striking the eyes of an observer, thereby greatly reducing the readability of the display.
In the case of the liquid-crystal display device disclosed in the Japanese Unexamined Patent Application publication H6-130424 as well, a color-selective layer that is directly visible-from the outside is a circular polarizer made of a cholesteric liquid crystal, which in the same manner as in Tokuhyo H4-512524, reflects approximately 50% of the light that strikes it, thereby causing a great reduction in readability.
While there was in the pasta dichroic circular polarizing layer (polarizer) of the light-absorbing type which absorbs light of one circular polarization direction and transmits light of another circular polarization direction, this was fabricated, for example, as a laminate of a xcex/4 phase-shifting layer made of a dichroic polarizing material such as Polaroid (TM), which transmits light polarized in the transmission axis direction and almost completely absorbs light having a polarization direction perpendicular to the light transmission axis direction, the xcex/4 phase-shifting layer causing either a lead or a lag of 45xc2x0 with respect to the light-absorption axis of the dichroic linear polarizing layer.
For this reason, a dichroic circular polarizer of the past functioned as a dichroic circuit polarizer only for light striking it from a dichroic linear polarizing layer, and did not function as such with respect to incident light from the opposite side.
Accordingly, it is an object of the present invention, in view of the above-described drawbacks in the related art, to provide a bidirectional dichroic circular polarizer that functions as a dichroic circular polarizer with respect to incident light from both directions.
Another object of the present invention is to provide a combination reflective/transmissive type liquid-crystal display device featuring high reflectivity and transmissivity, good readability, and which provides sufficient intensity, whether functioning as a transmissive-type display or a reflective-type display.
It is an additionally object of the present invention to provide a combination reflective/transmissive type liquid-crystal display device which has a simple configuration and which does not exhibit a loss of readability and a large decrease in contrast caused by external light, and which in the transmissive-type display mode particular, provides a great improvement in the utilization rate of light, and in the reflective display mode provides high contrast.
The above object is accomplished by means of a bidirectional dichroic circular polarizer according to the present invention comprising: a bidirectional linear polarizer on both sides of which are attached or directly formed quarter-wavelength layers.
The other object is accomplished by means of a combination reflective/transmissive liquid-crystal display device according to the present invention comprising:
a light source;
a polarization separation layer comprising one of a function of transmitting one direction of left or right circularly polarized light components incident from said light source or from an opposite direction and reflecting a circularly polarized light component of the opposite direction and a function of transmitting one direction component of linearly polarized light incident from said light source or from an opposite direction and reflecting a component of the other direction which is perpendicular thereto;
a half-wavelength layer, which, in response to on/off switching of a voltage either shifts incident polarized light from said polarization separation layer or from an opposite direction or does not shift said light;
a first light-absorbing type bidirectional dichroic polarization layer disposed on the opposite of the half-wavelength layer from the polarization separating layer, and comprising one of a function of transmitting, of light incident thereto from said half-wavelength layer or from the opposite direction, circularly polarized light of one of the left and right rotation directions and absorbing circularly polarize light of the other rotation direction, and a function of transmitting, of light incident thereto from said half-wavelength layer or from the opposite direction, linearly polarized light of only one direction, and absorbing linear polarized light of the direction perpendicular thereto;
a liquid-crystal layer that converts or does not convert one incident circularly polarized light or linearly polarized light to another circularly polarized light or linearly polarized light before it exits the opposite side, and comprises one of a function of changing the ellipticity when light exits with circular polarization and changing the polarization axis direction when light exits as linearly polarized light;
a second light-absorbing type bidirectional dichroic polarization layer disposed on the opposite of the liquid-crystal layer from the first bidirectional dichroic polarization layer, and comprising one of a function of transmitting, of light incident thereto from said liquid-crystal layer or from the opposite direction, circularly polarized light of one of the left and right rotation directions and absorbing circularly polarize light of the other rotation direction, and a function of transmitting, of light incident thereto from said liquid-crystal cell or from the opposite direction, linearly polarized light of only one direction, and absorbing linear polarized light of the direction perpendicular thereto;
wherein, by switching a voltage with respect to said half-wavelength layer on and off, it is possible to freely select between a reflective mode in which said display device operates in the reflective mode and a transmissive mode in which said display device operates in a transmissive mode, the configuration of the first bidirectional dichroic polarizing layer being such that said first bidirectional dichroic polarizing layer transmits polarized light having passed through said polarization separating layer,
and wherein when said half-wavelength layer is in the transmissive mode, polarized light having passed through said polarization separating layer is transmitted without a shift of phase, or with a shift of phase so that it is transmitted through the first bidirectional dichroic polarizing layer, but when said half-wavelength layer is in the reflective mode, the phase of polarized light having passed through said second bidirectional dichroic polarizing layer, said liquid-crystal layer, and said first bidirectional dichroic polarizing layer is shifted so that it is reflected by said phase shifting layer, or not shifted and also polarized light reflected from said phase shifting layer is shifted so as to be transmitted by the first bidirectional dichroic polarizing layer, or not shifted.
In the combination reflective/transmissive liquid-crystal display device, at least one of said first and second bidirectional dichroic polarizing layers may have a quarter-wavelength layer attached to or directly formed onto both sides thereof.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a circular polarization separating layer that, of the incident light, transmits either right or left rotated circularly polarized light, and reflects circularly polarized light of the other direction;
said first and second bidirectional dichroic polarizing layers are light-absorbing type bidirectional dichroic circularly polarizing layers that, of the incident light, transmit either right or left rotated circularly polarized light, and absorb circularly polarized light of the other direction; and
electrodes are provided on said liquid-crystal layer for applying an electrical field thereto, an electrical field being applied from the electrodes to the liquid-crystal layer so as to change the retardation value thereof, so that the phase of circularly polarized light incident via transmission through the first bidirectional dichroic polarizing layer or circularly polarized light incident via transmission through the second bidirectional dichroic polarizing layer is substantially shifted 0 to xcfx80.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a linear polarization separating layer that, of the incident light, ransmits only one linearly polarized light component, and reflects linearly polarized light of the other direction;
said first and second bidirectional dichroic polarizing layers are light-adsorbing type bidirectional dichroic linearly polarizing layers that, of the incident light, transmit only one linearly polarized light component, and absorb linearly polarized light of the other direction; and
electrodes are provided on said liquid-crystal layer for applying an electrical field thereto, an electrical field being applied from the electrodes to the liquid-crystal layer so as to change the retardation value thereof, so that the phase of linearly polarized light incident via transmission through the first bidirectional dichroic polarizing layer or linearly polarized light incident via transmission through the second bidirectional dichroic polarizing layer is substantially shifted 0 to xcfx80.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a circular polarization separating layer that, of the incident light, transmits either right or left rotated circularly polarized light, and reflects circularly polarized light of the other direction;
said first bidirectional dichroic polarizing layer is light-absorbing type bidirectional dichroic circularly polarizing layers that, of the incident light, transmit either right or left rotated circularly polarized light, and absorb circularly polarized light of the other direction;
said second bidirectional dichroic polarizing layer is light-absorbing type bidirectional dichroic linearly polarizing layers that, of the incident light, transmit only one linearly polarized light component, and absorb linearly polarized light of the other direction; and
electrodes are provided on said liquid-crystal layer for applying an electrical field thereto, an electrical field being applied from the electrodes to the liquid-crystal layer so as to change the retardation value thereof, so that the phase of circularly polarized light incident via transmission through the first bidirectional dichroic polarizing layer or linearly polarized light incident via transmission through the second bidirectional dichroic polarizing layer is substantially shifted xe2x88x92xcfx80/2 to xcfx80/2.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a linear polarization separating layer that, of the incident light, transmits only one linearly polarized light component, and reflects linearly polarized light of the other direction;
said first bidirectional dichroic polarizing layer is light-absorbing type bidirectional dichroic linearly polarizing layers that, of the incident light, transmit only one linearly polarized light component, and absorb linearly polarized light of the other direction;
said second bidirectional dichroic polarizing layer is light-absorbing type bidirectional dichroic circularly polarizing layers that, of the incident light, transmit either right or left rotated circularly polarized light, and absorb circularly polarized light of the other direction; and
electrodes are provided on said liquid-crystal layer for applying an electrical field thereto, an electrical field being applied from the electrodes to the liquid-crystal layer so as to change the retardation value thereof, so that the phase of linearly polarized light incident via transmission through the first bidirectional dichroic polarizing layer or linearly polarized light incident via transmission through the second bidirectional dichroic polarizing layer is substantially shifted xe2x88x92xcfx80/2 to xcfx80/2.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a circular polarization separating layer that, of the incident light, transmits either right or left rotated circularly polarized light, and reflects circularly polarized light of the other direction;
said first bidirectional dichroic polarizing layer is a light-absorbing type bidirectional dichroic circular polarizing layer that, of the incident light, transmits either right or left rotated circularly polarized light, and absorbs circularly polarized light of the other direction;
said second bidirectional dichroic polarizing layer is a light-absorbing type bidirectional dichroic linearly polarizing layer that, of the incident light, transmits only one linearly polarized light component, and absorbs linearly polarized light of the other direction;
said liquid-crystal layer has a retardation value that substantially shifts transmitted light xcfx80/2 and is provided with electrodes for applying an electrical field thereto, the action of which is that circularly polarized light incident via transmission through said first bidirectional dichroic polarizing layer or linearly polarized light incident via transmission through said second bidirectional dichroic polarizing layer is converted to linearly polarized light or circularly polarized light before it exits on the opposite side, an electrical field being applied to the liquid-crystal layer from said electrode, so that the direction of the director of the liquid crystal is changed, thereby changing the polarization axis of the linearly polarized light or circularly polarized light.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a linear polarization separating layer that, of the incident light, transmits only one linearly polarized light component, and reflects linearly polarized light of the other direction;
said first bidirectional dichroic polarizing layer is a light-absorbing type bidirectional dichroic linearly polarizing layer that, of the incident light, transmits only one linearly polarized light component, and absorbs linearly polarized light of the other direction;
said second bidirectional dichroic polarizing layer is a light-absorbing type bidirectional dichroic circular polarizing layer that, of the incident light, transmits either right or left rotated circularly polarized light, and absorbs circularly polarized light of the other direction;
said liquid-crystal layer has a retardation value that substantially shifts transmitted light xcfx80/2 and is provided with electrodes for applying an electrical field thereto, the action of which is that linearly polarized light incident via transmission through said first bidirectional dichroic polarizing layer or circularly polarized light incident via transmission through said second bidirectional dichroic polarizing layer is converted to circularly polarized light or linearly polarized light before it exits on the opposite side, an electrical field being applied to the liquid-crystal layer from said electrodes, so that the direction of the director of the liquid crystal is changed, thereby changing the polarization axis of the circularly polarized light or linearly polarized light.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a linear polarization separating layer that, of the incident light, transmits one linearly polarized light component, and reflects linearly polarized light of the other direction;
said first and second bidirectional dichroic polarizing layers are light-absorbing type bidirectional dichroic linearly polarizing layers that, of the incident light, transmit one linearly polarized light component and absorb linearly polarized light of the other direction;
said liquid-crystal cell having a retardation value that substantially shifts transmitted light xcfx80, and is provided with electrodes for applying an electrical field thereto, the action of which is to change the rotation of light by application of the electrical field, so that the polarization plane of linearly polarized light incident via transmission through said first or second bidirectional dichroic polarizing layer is shifted as it exits from the liquid-crystal layer.
The combination reflective/transmissive liquid-crystal display device may be, wherein:
said polarization separating layer is a linear polarization separating layer that, of the incident light, transmits one linearly polarized light component, and reflects circularly polarized light of the other direction;
said first and second bidirectional dichroic polarizing layers are light-absorbing type bidirectional dichroic linearly polarizing layers that, of the incident light, transmit one linearly polarized light component and absorb linearly polarized light of the other direction;
said liquid-crystal cell having a retardation value that substantially shifts transmitted light xcfx80, and is provided with electrodes for applying an electrical field thereto, the action of which is to change the rotation of light by application of the electrical field, so that the polarization plane of linearly polarized light incident via transmission through said first or second bidirectional dichroic polarizing layer is shifted as it exits from the liquid-crystal layer.
The combination reflective/transmissive liquid-crystal display device may be, wherein said liquid-crystal layer is sandwiched between two substrates, said substrates being formed on one of said electrodes, so that the electrical field direction when a voltage is applied to said electrode has a part that is substantially parallel with the surface of said substrates, the direction of liquid crystal molecules within the liquid-crystal layer rotating while remaining substantially parallel to said substrate surfaces.
The combination reflective/transmissive liquid-crystal display device may be, wherein said circular polarization separating layer is made of a rotation selection film made of a cholesteric liquid crystal.
The combination reflective/transmissive liquid-crystal display device may be, wherein said circular polarization separating layer comprises a lamination of a phase shifting layer having a retardation value that causes a substantial shift of xcfx80/2 to the phase of transmitted light, and at least three films exhibiting birefringence, wherein the difference in the refractive index between the layers adjacent to each other along its thickness direction for one of two light beams having vibration directions perpendicular to each other in a plane being different from the difference in the refractive index between the layers adjacent to each other along its thickness direction for the other light beams.
The combination reflective/transmissive liquid-crystal display device may be, wherein the linear polarization separating layer has a planar laminated structure having three or more layers each of which has double refraction; and the difference in the refractive index between the layers adjacent to each other along its thickness direction for one of two light beams having vibration directions perpendicular to each other in a plane is different from the difference in the refractive index between the layers adjacent to each other along its thickness direction for the other of the two light beams.
The combination reflective/transmissive liquid-crystal display device may be, wherein said linear polarization separating layer comprises a phase shifting layer having a retardation value that causes a substantial shift of xcfx80/2 to the phase of transmitted light, and a rotation-selecting layer made of a cholesteric liquid crystal, wherein circularly polarized light transmitted by said cholesteric liquid crystal is converted to linearly polarized light.
The combination reflective/transmissive liquid-crystal display device may be, wherein said half-wavelength layer is formed by a liquid-crystal cell including a liquid-crystal layer, liquid crystal in liquid crystal cell being one type selected from a group consisting of nematic liquid crystal, ferroelectric liquid crystal, and anti-ferroelectric liquid crystal, and wherein the refractive index and thickness of the liquid crystal is established so as to shift polarized light incident thereto by xcfx80.
The combination reflective/transmissive liquid-crystal display device may be, further comprising a switch as means for switching said half-wavelength layer on and off.
The combination reflective/transmissive liquid-crystal display device may be, further comprising a switch as means for switching said half-wavelength layer on and off, and an external light sensor that detects an amount of external light and sets said switch to on or off when said light amount exceeds a prescribed value, and sets said switch to off or on when said light amount is below said prescribed value.
The combination reflective/transmissive liquid-crystal display device may be, wherein said half-wavelength layer and a first bidirectional dichroic polarizing layer between the liquid-crystal layer in said liquid crystal layer of said half-wavelength layer are laminated, together with said liquid-crystal layer between a pair of substrates making up said liquid-crystal cell.
In a bidirectional dichroic circular polarizer according to the present invention, it is possible to absorb incident light having a circular polarization of one direction, and to transmit incident light having circular polarization of another direction.
In a liquid-crystal display device according to the present invention, by using a combination of a polarization separation layer, a half-wavelength layer, a bidirectional dichroic polarization layer, and a liquid-crystal cell, it is possible to achieve sufficient intensity and readability, regardless of whether the liquid-crystal display device is operating in the reflective mode or the transmissive mode.
The present invention provides a liquid-crystal display device which makes use of a light-absorbing type bidirectional dichroic polarizing;layer at a surface visible from the outside, the retardation value of a liquid-crystal layer being changed in accordance with this dichroic polarizing layer, thereby making use of the birefringence of the liquid-crystal layer so as to achieve good contrast, without a decrease in the utilization rate of light or a decrease in contrast caused by external light, thereby preventing a worsening of the readability of the display.